The present invention relates to a flow type particle image analyzing method and apparatus in which a sample fluid containing suspended particles flowing in a flat style continuously and then imaged in order to analyze the particles in the sample fluid. More particularly, this invention relates to a flow type particle image analyzing method and apparatus suitable for analysis of cells or particles contained in blood or urine.
In a conventional analyzation, cells existing in blood or cells or particles existing in urine have been categorized and analyzed by mounting specimens on slides and observing them under a microscope. As far as urine is concerned, since a concentration of particles in urine is low, a sample is centrifuged and condensed using a centrifuge for later observation. In an apparatus for automating these observation and examination work, a slide is smeared with a sample of blood or the like and set in a microscope, a stage in the microscope is automatically scanned over the slide and stopped at locations of particles in order to produce still images of the particles, and then image processing techniques of characteristic extraction and pattern recognition are used to categorize the particles in the sample.
However, the foregoing procedure requires much time for mounting specimens. Moreover, extra work is required to find out particles while moving the stage of a microscope mechanically and move the particles to an image pickup zone. Achieving this work makes analysis time-consuming and machinery complex.
In an effort to improve examination precision and save labor, a flow type particle image analyzing apparatus using a flow chamber in which a sheathing solution that is a purity solution is used as an outer layer in order to provide a very flat flow of a sample fluid has been disclosed in, for example, JP,A,57-500995, JP,A,63-94156, or JP,A,4-72544.
In the flow type particle image analyzing apparatus, a sample fluid moving in the flow chamber is imaged using, for example, a video camera. Produced still images are then processed in order to categorize or count particles in the sample.
A flow type particle image analyzing apparatus for imaging particles in a sample by changing powers has been described as a particle analyzer in U.S. Pat. No. 5,088,816(JP,A,3-105235) and JP,A,4-309841.
The particle analyzer described in the U.S. Pat. No. 5,088,816 and JP,A,4-309841 comprises a strobe for continuously emitting light that flashes for a short period of time, a diaphragm for adjusting an amount of flashlight from the strobe, a diffuser screen for resolving irregularity in luminous intensity of flashlight, a condenser lens for converging flashlight, a flow chamber positioned in the passage of flashlight and designed to provide a flat flow of a sample fluid while enclosing the sample fluid with a sheathing solution, an objective lens for forming images of particles irradiated by flashlight, a high-power projection lens, a low-power projection lens, a TV camera for shooting images, a means for moving the diffuser screen, a means for varying the size of an aperture stop, and a switching means for switching the high-power and low-power projection lenses.
In the flow chamber, a fluid path for a sample fluid has a cross section that tapers in a direction of flow and expands gradually in a direction substantially orthogonal to a direction in which flashlight travels from the vicinity of an entry of an imaging zone toward an exit thereof. This is intended to control postures of flat particles so that flat surfaces of the flat particles will be substantially orthogonal to flashlight and to produce images representing the characteristics of the particles.
In the foregoing particle analyzer, the projection lenses are switched so that an optimal power will be specified according to the diameters of particles to be measured. Thus, analysis can be undertaken. When the projection lenses are switched, depths of focus are changed. The ratio of a flow rate of a sample fluid flowing into the flow chamber to a flow rate of a sheathing solution flowing thereinto is then modified according to a designated depth of field, whereby the sample fluid is changed in thickness.
To be more specific, when the diameters of particles in a sample to be measured are small (about 10 micrometers), the high-power (for example, power 40) projection lens is selected. A smaller depth of focus is designated accordingly. For a high power, therefore, a sample fluid is made thin.
When the diameters of particles in a sample to be measured are large (about several tens of micrometers), the low-power (for example, power 10) projection lens is selected. A large depth of focus is designated accordingly. For a low power, therefore, a sample fluid is made thick.